1. Field of the Invention
This invention relates generally to rhodium catalyzed hydroformylation of olefins and more specifically to an improved hydroformylation process for alpha-substituted alpha-olefins using homogeneous rhodium catalyst systems containing highly sterically hindered tricycloalkyl phosphine ligands.
2. Description of the Prior Art
The hydroformylation of olefins to aldehydes is a widely used industrial process in which an olefin, carbon monoxide and hydrogen, are reacted in the presence of a homogeneous hydroformylation catalyst. These catalysts have historically comprised high pressure cobalt systems. Recent developments of low pressure rhodium catalyst systems have been the subject of a considerable body of patent art and literature, and rhodium-triphenyl phosphine systems have been widely, and successfully, used commercially for the hydroformylation of propylene feedstocks to produce butyraldehyde.
A large variety of trialkyl phosphines have been suggested for use in rhodium catalyzed hydroformylation of olefins. U.S. Pat. No. 3,168,533 relates to the hydroformylation of olefins (including alpha and internal monoolefins and diolefins) using Group VIIIb transition metal (Co, Ru, Rh and Ir) catalyst systems and triorganophosphorus ligands including trivalent phosphorus compounds having aliphatic, cycloaliphatic, heterocyclic and/or aromatic radicals satisfying the three valences of the trivalent phosphorus atom, at preferred carbon monoxide pressures of 5500 to 21,000 kPa (or higher) at temperatures of 75.degree. to 250.degree. C.
U.S. Pat. No. 3,239,566 also relates to the Rh and Ru catalyzed hydroformylation employing a tertiary organo-phosphine (e.g., trialkyl and tricycloalkyl phosphines, such as tricyclopentyl and tricyclohexyl phosphines) at 100.degree. to 300.degree. C. and total pressures of 690 to 13,800 kPa, using terminally- or internally-unsaturated olefins as feedstock.
U.S. Pat. No. 3,511,880 discloses the hydroformylation of alpha-olefins and internal-olefins employing a partially aqueous high boiling inert organic reaction medium containing a Group VIII noble metal biphyllic ligand complex as the catalyst and containing an alkaline material such as ammonium or alkali metal hydroxide. Suitable biphyllic ligands are said to include trialkyl phosphines, and tricyclohexyl phosphine and phenyldiisopropyl phosphine are disclosed as suitable. Reaction temperatures of 50.degree. to 200.degree. C., and reaction pressures of 100-30,400 kPa are employed. U.S. Pat. No. 3,965,192 is similar in its disclosure to U.S. Pat. No. 3,511,880, as to suitable triorgano phosphines.
U.S. Pat. No. 3,527,809 relates to a process for hydroformylation of alpha-olefins using triaryl phosphines (having a .DELTA.HNP value of at least 425) in combination with rhodium catalyst, at a total pressure of less than 3100 kPa and at temperatures of 50.degree. to 145.degree. C. Triisopropyl phosphine ligand is disclosed to be an unsuitable ligand due to its low .DELTA.HNP value. Also excluded were trialkyl phosphines and tricycloalkyl phosphines.
U.S. Pat. No. 4,201,728 discloses highly selective alpha-olefin hydroformylation catalysts comprising a stabilized rhodium complex containing a bidentate ligand and a monodendate ligand, which is characterized by cyclindrical cone angle .theta. of between about 135.degree. and 150.degree.. The reactions are carried out at from 25.degree. to 150.degree. C. and at 103 to 20,700 kPa.
Alpha-substituted alpha-olefins, similar to internal olefins, are known to be much less reactive than terminal olefins for hydroformylation. For example, U.S. Pat. No. 4,221,744 (column 15, lines 40-60) indicates that the internal olefin is relatively inert under the conditions of all of its preceding examples, and the relative inertness of alpha-substituted alpha-olefins (isobutylene) is also taught in U.S. Pat. No. 4,287,370 (under its conditions, in which a mixed butene feedstock is contacted with a rhodium triorganophosphine ligand system, in which the ligand can be trialkylphosphine (column 5, lines 29-30).
U.S. Pat. No. 3,576,881 (column 5, lines 20-23) teaches that biphyllic triorganophosphorus ligands having cycloaliphatic groups, do not form active catalyst species for Fe, Co and Rh catalyzed olefin hydroformylations. The reference, therefore, employs trialkyl and trialkoxy phosphorus ligands.
B. Fell et al., Tetrahedron Letters No. 29, pp. 3261-3266 (1968) conducted studies on olefin isomerizations during the hydroformylation of higher molecular weight olefins with complex cobalt and rhodium catalysts. Trialkyl phosphines were found to suppress olefin isomerization without suppressing hydroformylations, in hydroformylation of 1-octene and trans-octene-4 in an agitated autoclave at 20,270 kPa and 140.degree. C. (using 1:1 CO:H.sub.2) to greater than 90% theoretical yield, using Rh2.sup.O.sub.3 with either tricylcohexyl phosphine or tri-n-butyl phosphine (Table 2). N-hexenoic-3-acid-1-methyl ester was hydroformylated at 120.degree. C. under similar conditions using a Rh catalyst system containing tricyclohexyl phosphine (Table 5). However, with four hours of reaction time, assuming complete conversion, the hydroformylation rates for tricyclohexyl phosphine (using a Rh concentration of 1.75 mmol Rh per mole of olefin charged) corresponded to a catalyst turnover of only 142.9 moles olefin/mole Rh/hour. Therefore, Fell et al. reported similar performance for tricyclohexyl phosphine and tri-n-butyl phosphine in Rh hydroformylation catalyst systems, no distinction in aldehyde production rates being observed. The Fell et al. experiments are also discussed in F. Asinger et al., I&EC Prod. Res. & Dev., vol. 8, no. 2, 214 (1969) and E. R. Tucci, I&EC Prod. Res. & Dev., vol. 8, no. 2, 215-26 (1969).
B. Fell et al., J. Molec. Catalysis, vol. 2, 211-218 (1977) investigated the hydroformylation of conjugated dienes using certain aliphatic tertiary phosphines (including tris-isopropyl phosphine) at specified conditions.
German Pat. No. 2,538,364, as abstracted in 85 Chem. Abs. 45,962m, reported no difference in results in the rhodium catalyzed hydroformylation of allyl alcohol with tris-triphenyl phosphine, tri-n-butyl phosphine, tricyclohexyl phosphine and 4-methyl benzene.
Van Leewen and Roobeek, J. Organomet. Chem., vol. 258, pp. 343-350 (1983) investigated the hydroformylation of 2-alkyl-1-alkenes and cyclohexene with bulky phosphite ligands, and reported low rates of reaction when using tricyclohexyl phosphine as the ligand of the rhodium catalyst system.
U.S. Pat. No. 4,443,638 relates to a process for preparing alcohols from internal olefins including the step of hydroformylating internal olefins to aldehydes using a small amount of a recycled rhodium catalyst which is "ligand modified". Suitable ligands which are disclosed are the trialkylphosphites, tricyloalkyl phosphites, triarylphosphites, triarylphosphines, trialkyl phosphines, triarylstilbines and triaryl arsines. Temperatures of 145.degree. to 180.degree. C. and pressures of about 5,100 to 13,800 kPa are used in the hydroformylation. The recycled rhodium catalyst is separated from the hydroformylation reaction product by flash distillation, prior to the catalyst's recycle to the hydroformylation reactor.
European Patent Application No. 28,378 relates to an improved rhodium-catalyzed hydroformylation process wherein the catalyst stability is improved by use of a ligand selected from a branched chain alkyl diphenylphosphine, a branched chain dialkyl-phenylphosphine, a cycloalkyldiphenylphosphine, and a dicycloalkylphenylphosphine. European Patent Application No. 96,988 relates to a hydroformylation process for producing non-linear aldehydes from optionally substituted internal olefins, using a certain class of cyclic phosphite ligands.
A. A. Oswald et al., Preprint of Papers, American Chemical Society (Seattle Meeting, March 20-25, 1983), vol. 2, no. 2, pp. 191-208 reports the rhodium catalyzed hydroformylation of 1-butene using branched alkyl diphenyl phosphine ligands, including cyclohexyl diphenyl phosphine.